Transceiver for communication and method for controlling communication

ABSTRACT

In an example embodiment, a communication system provides a clock extension peripheral interface (CXPI) communication bus that is coupled to a master node and a plurality of slave nodes. The master node is configured to transmit a reference clock signal on the CXPI communication bus. Each slave node of the plurality of slave nodes is configured to receive the reference clock signal from the CXPI communication bus and to transmit and receive data to and from the CXPI communication bus based on the reference clock signal.

PRIORITY

The present application is a continuation application of U.S. Non-Provisional application Ser. No. 16/392,405, filed on Apr. 23, 2019, which is a continuation application of U.S. Non-Provisional application Ser. No. 16/045,460, filed on Jul. 25, 2018, now U.S. Pat. No. 10,361,793, issued on Jul. 23, 2019, which is a continuation of U.S. Non-Provisional application Ser. No. 15/449,558, filed on Mar. 3, 2017, now U.S. Pat. No. 10,063,325, issued on Aug. 28, 2018 which is a continuation of U.S. Non-Provisional application Ser. No. 15/198,928, filed on Jun. 30, 2016, now U.S. Pat. No. 9,705,697, issued on Jul. 11, 2017, which claims the priority and benefit of U.S. Provisional Application No. 62/307,925, filed on Mar. 14, 2016, the entire contents of which are incorporated by reference herein in their entirety.

TECHNICAL FIELD

This disclosure relates to a transceiver for communication and a method for controlling communication.

BACKGROUND

In an apparatus provided with a plurality of electronically controllable devices, communication is performed between processors that individually control the devices. For example, a vehicle such as an automobile is provided with an air conditioner, door mirrors, power windows, wipers, and other electronically controllable devices. A plurality of Electronic Control Units (ECU) that electronically control these devices are mounted in the vehicle. These ECUs are connected to each other by a bus and communicate according to a predetermined communication protocol.

During communication between the ECUs, noise might be emitted by wiring in the bus that connects the ECUs. The emitted noise might affect other devices depending on the frequency band.

SUMMARY

It would therefore be helpful to provide a transceiver for communication and a method for controlling communication that can reduce the effect of noise.

To this end, a transceiver for communication according to one aspect of this disclosure includes a timing determiner configured to detect a fall from high level to low level of a bus signal generated by pulse width modulation of a clock signal and input from a communication bus; a transmission data signal delay adjuster configured to determine a second timing having a predetermined time difference from a first timing, the bus signal rising from the low level to the high level at the first timing; an encoder configured to extend a low level of the bus signal by changing a data signal to be output to the communication bus from high level to low level; and a timing adjustment circuit configured to change the data signal to the low level at the second timing.

In the above aspect, the transmission data signal delay adjuster may calculate the predetermined time difference with Equation (1) below: t _(diff)=(2n−1)/(2f _(notch))  (1)

where t_(diff) is the predetermined time difference, f_(notch) is a frequency at which a harmonic level is reduced, and n is a natural number.

The above aspect may further include a clock rise start detector configured to detect a start of rising from the low level of the bus signal; and a clock rise start determiner configured to determine the first timing based on a timing of the start of rising of the bus signal from the low level detected by the clock rise start detector.

The above aspect may further include a first comparator configured to compare a signal level of the bus signal with a first reference voltage; a second comparator configured to compare the signal level with a second reference voltage different from the first reference voltage; and a clock rise start determiner configured to determine a timing of a start of rising from the low level of the bus signal based on a comparison result from the first comparator and the second comparator.

In the above aspect, the transmission data signal delay adjuster may determine the second timing to be after the fall of the bus signal.

The above aspect may further include a first comparator configured to compare a signal level of the bus signal with a first reference voltage; a second comparator configured to compare the signal level with a second reference voltage different from the first reference voltage; and a clock fall end determiner configured to determine a timing of the fall of the bus signal based on a comparison result from the first comparator and the second comparator.

In the above aspect, the transmission data signal delay adjuster may determine the second timing to be earlier than a timing of a start of rising from the low level of the bus signal.

In the above aspect, the transmission data signal delay adjuster may determine a timing of a start of rising from the low level to the high level of the data signal to be a predetermined length of time after a timing of the fall of the bus signal.

In the above aspect, the transceiver for communication may be included in a node used in Clock Extension Peripheral Interface (CXPI) communication.

In the above aspect, the transceiver for communication may function as a slave node transceiver communicating with a master node transceiver over the communication bus (e.g., such as a CXPI bus).

According to another aspect of this disclosure, a method is provided for controlling communication by a transceiver that communicates over a communication bus, the method including: detecting a fall from high level to low level of a bus signal generated by pulse width modulation of a clock signal and input from the communication bus; determining a second timing having a predetermined time difference from a first timing, the bus signal rising from the low level to the high level at the first timing; extending a low level of the bus signal by changing a data signal to be output to the communication bus from high level to low level; and changing the data signal to the low level at the second timing.

In the above aspect, the predetermined time difference may be calculated with Equation (2) below: t _(diff)=(2n−1)/(2f _(notch))  (2)

where t_(diff) is the predetermined time difference, f_(notch) is a frequency at which a harmonic level is reduced, and n is a natural number.

The above aspect may further include detecting by a clock rise start detector a start of rising from the low level of the bus signal; and determining the first timing based on a timing of the bus signal detected by the clock rise start detector.

In the above aspect, the transceiver for communication may include a first comparator and a second comparator, and the above aspect may further include: the first comparator comparing a signal level of the bus signal with a first reference voltage; the second comparator comparing the signal level with a second reference voltage different from the first reference voltage; and determining a timing of a start of rising from the low level of the bus signal based on a comparison result from the first comparator and the second comparator.

The above aspect may further include determining the second timing to be after the fall of the bus signal.

In the above aspect, the transceiver for communication may include a first comparator and a second comparator, and the above aspect may further include: the first comparator comparing a signal level of the bus signal with a first reference voltage; the second comparator comparing the signal level with a second reference voltage different from the first reference voltage; and determining a timing of the fall of the bus signal based on a comparison result from the first comparator and the second comparator.

The above aspect may further include determining the second timing to be earlier than a timing of a start of rising from the low level of the bus signal.

The above aspect may further include determining a timing of a start of rising from the low level to the high level of the data signal to be a predetermined length of time after a timing of the fall of the bus signal.

In the above aspect, the transceiver for communication may be included in a node used in Clock Extension Peripheral Interface (CXPI) communication.

In the above aspect, the transceiver for communication may function as a slave node transceiver communicating with a master node transceiver over the communication bus (e.g., such as CXPI bus).

The transceiver for communication and the method for controlling communication of the embodiments below can reduce the effect of noise.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 illustrates the relationship between control by a slave node and current flowing in the communication bus;

FIG. 2 illustrates an example of the spectrum of harmonic levels when executing control according to one of the disclosed embodiments;

FIG. 3 is a block diagram illustrating an example of a transceiver for communication according to this embodiment;

FIG. 4 illustrates an example of controlling a transmission data signal with the transceiver for communication according to this embodiment;

FIG. 5 illustrates the change in current of the communication bus when the slave fall end is sooner than the clock fall end;

FIG. 6 is a block diagram illustrating an example of a transceiver for communication according to a modification to this embodiment;

FIG. 7 illustrates a method of determining the time of the rise start and the time of the clock fall end in the transceiver for communication of FIG. 6;

FIG. 8 illustrates processing by the clock fall end determiner in FIG. 6 for determining the time of the clock fall;

FIG. 9 illustrates an example of a method by which the transmission data signal delay adjuster in FIG. 6 determines the delay time;

FIG. 10 illustrates an example of a method by which the transmission data signal delay adjuster in FIG. 6 determines the delay time;

FIG. 11 illustrates a transmission data signal and a bus signal controlled by the decoder in FIG. 6;

FIG. 12 illustrates a transmission data signal and a bus signal controlled by the decoder in FIG. 6;

FIG. 13 illustrates the change in current of the communication bus when the rise start is sooner than the slave fall end;

FIG. 14 illustrates an example of the system structure in CXPI communication;

FIG. 15 illustrates an example of the circuit structure in a CXPI communication system;

FIG. 16 illustrates an example of the waveform for the master node in a CXPI communication system;

FIG. 17 illustrates a portion of the circuit within the CXPI transceiver of the master node in FIG. 15;

FIG. 18 illustrates an example of the waveform for the slave node in a CXPI communication system;

FIG. 19 illustrates an example of the spectrum of noise generated in a CXPI communication system;

FIG. 20 illustrates an example of voltage on the communication bus;

FIG. 21 illustrates an example of current flowing in the communication bus;

FIG. 22 schematically illustrates an example of current flow in the communication bus; and

FIG. 23 illustrates an example of the case when the inclination of the fall is set to be identical in the bus signal output by the master node and the bus signal output by the slave node.

DETAILED DESCRIPTION

Examples of communication protocols used between ECUs mounted in an automobile include a Local Interconnect Network (LIN), a Controller Area Network (CAN), and a Clock Extension Peripheral Interface (CXPI).

As illustrated by the example in FIG. 14, a communication system 1400 that performs CXPI communication includes one master node 1401 and a plurality of slave nodes 1402. FIG. 14 illustrates an example with three slave nodes 1402. The master node 1401 is connected to each slave node 1402 by a communication bus 1403. The master node 1401 and the slave nodes 1402 are, for example, each configured with a computer, computing device, or the like.

The master node 1401 is a node that controls the operation timing of each slave node 1402. The master node 1401 transmits a bus signal mBUS (see FIG. 15), which becomes the reference for communication, at a constant frequency to the communication bus 1403. The slave nodes 1402 transmit and receive data with the bus signal mBUS transmitted by the master node 1401 as a reference clock.

FIG. 15 illustrates an example of the circuit structure in a CXPI communication system. FIG. 15 only illustrates one slave node 1504 in order to simplify the illustration. A master node 1501 includes a microcontroller 1502 and a CXPI transceiver 1503. The slave node 1504 includes a microcontroller 1505 and a CXPI transceiver 1506. The microcontrollers 1502 and 1505 each include a Universal Asynchronous Receiver Transmitter (UART) interface and each transmit and receive signals to and from the CXPI transceivers 1503 and 1506.

In CXPI communication, the master node 1501 transmits data by subjecting the clock signal mCLK to Pulse Width Modulation (PWM). FIG. 16 illustrates an example of the waveform for the master node in a CXPI communication system. FIG. 16 illustrates the clock signal mCLK output from the microcontroller 1502 to the CXPI transceiver 1503, a data signal mTXD output from the microcontroller 1502 to the CXPI transceiver 1503, and the bus signal mBUS output by the CXPI transceiver 1503 to a communication bus 1507.

A CXPI transceiver 1503 performs PWM on the clock signal mCLK to generate a signal exhibiting a logical value corresponding to the data signal mTXD. The bus signal mBUS generated by performing PWM on the clock signal mCLK is transmitted to the slave node 1504, thereby transmitting data from the master node 1501 to the slave node 1504. The bus signal mBUS has two voltage levels (high level and low level). The high level and the low level of the bus signal mBUS are generated by a circuit such as the one illustrated in FIG. 17 and are output to the communication bus 1507. The high level of the bus signal mBUS is determined by a pull-up resistor 1701 connected to a power line. The low level of the bus signal mBUS is generated by an output terminal to the communication bus 1507 being connected to a ground GND via a transistor Tr controlled by the data signal mTXD being input.

In CXPI communication, the logical value of the bus signal mBUS output to the communication bus 1507 is determined by the length of the low level (or the high level) of the bus signal mBUS. When the duration of the low level of the bus signal mBUS is shorter than a predetermined time, for example in the intervals Z₁ and Z₂ in FIG. 16, the logical value of the bus signal mBUS is 1. When the duration of the low level of the bus signal mBUS is longer than a predetermined time, for example in the interval Z₃ in FIG. 16, the logical value of the bus signal mBUS is 0.

The CXPI transceiver 1503 performs PWM on the clock signal mCLK so that the bus signal mBUS exhibits a logical value of 1 when the data signal mTXD is at a high level, as shown in the intervals Z₁ and Z₂ in FIG. 16. Conversely, by extending the duration of the low level of the bus signal mBUS, the CXPI transceiver 1503 performs PWM on the clock signal mCLK so that the bus signal mBUS exhibits a logical value of 0 when the data signal mTXD is at a low level, as shown in the interval Z₃ in FIG. 16. In this way, the CXPI transceiver 1503 transmits data by controlling the logical value of the bus signal mBUS based on the data signal mTXD.

The CXPI transceiver 1503 receives a bus signal sBUS transmitted by the slave node 1504 from the communication bus 1507 and transmits a data signal obtained by decoding the bus signal sBUS to the microcontroller 1502 as a received signal mRXD.

The slave node 1504 transmits data by combining the bus signal sBUS with the bus signal mBUS output by the master node 1501 to generate the bus signal BUS. At the timing at which the slave node 1504 outputs data, the master node 1501 does not transmit data but rather transmits the bus signal mBUS at a constant duty cycle and receives the bus signal sBUS transmitted by the slave node 1504 from the communication bus 1507. At the timing at which the slave node 1504 outputs data, the bus signal mBUS output by the master node 1501 is a signal with a logical value of 1. In other words, when the slave node 1504 does not output the bus signal sBUS, the bus signal BUS exhibits a logical value of 1. When outputting the bus signal sBUS, the slave node 1504 configures the bus signal sBUS so that the logical value of the combined bus signal BUS will be 0. By the slave node 1504 thus determining the logical value of the combined bus signal BUS based on the bus signal sBUS, data can be transmitted to the master node 1501 that acquires the bus signal BUS.

FIG. 18 illustrates an example of the waveform for the slave node in the CXPI communication system. FIG. 18 illustrates a bus signal BUS that is a combination of the bus signal sBUS output from the slave node 1504 (CXPI transceiver 1506) and the bus signal mBUS output from the master node 1501, a data signal sTXD output by the microcontroller 1505, a received data signal RXD acquired by the CXPI transceiver 1506 from the bus signal mBUS, and a transmission data signal TXD transmitted by the CXPI transceiver 1506 to the communication bus 1507.

The slave node 1504 receives the bus signal mBUS output from the master node 1501 via the communication bus 1507 and operates. The CXPI transceiver 1506 acquires the clock signal sCLK from the bus signal mBUS acquired from the communication bus 1507 and outputs the clock signal sCLK to the microcontroller 1505.

When transmitting data to the communication bus 1507, the slave node 1504 notifies other nodes of the start of data transmission by driving the bus signal mBUS acquired from the master node 1501. Transmission of data by the slave node 1504 is now described. The CXPI transceiver 1506 detects a fall in the bus signal mBUS by a change (fall) in the received data signal RXD, which is generated by a circuit inside the CXPI transceiver 1506 and the logical value of which changes in accordance with behavior of the bus signal mBUS ((i) in FIG. 18). Upon detecting a fall in the bus signal mBUS by a fall in the received data signal RXD, the CXPI transceiver 1506 controls the logical value of the transmission data signal TXD generated in a circuit inside the CXPI transceiver 1506 to be 0 based on the data signal sTXD output by the microcontroller 1505 ((ii) in FIG. 18). Upon the transmission data signal TXD being input into the communication bus 1507, the voltage of the bus signal sBUS drops to the low level while the logical value of the transmission data signal TXD is 0. Therefore, the duration of low level of the bus signal BUS that is the combination of the bus signal mBUS and the bus signal sBUS is extended ((iii) in FIG. 18). In this way, by the low level of the bus signal BUS being extended, the master node 1501 can receive a bus signal BUS with an extended low level, thereby detecting the start of data transmission from the slave node 1504 to the master node 1501 and starting to receive data.

As described above, when communication is performed between the master node 1501 and the slave node 1504, noise may be emitted from the communication bus 1507 by transmission and reception of signals. The noise emitted from the communication bus 1507 may affect other communication. For example, a smart key system is affected by noise. A smart key system is a system whereby a key that the user possesses locks and unlocks doors of the automobile by wireless communication with the automobile. For example, when using a 19.2 kHz signal as the reference clock in CXPI communication and using a 134 kHz signal in the smart key system, 134 kHz is the 7th harmonic of 19.2 kHz. Therefore, as illustrated in FIG. 19, the harmonic level around 134 kHz (100 kHz to 160 kHz) indicated by region 1900 in the noise frequency spectrum increases. As a result, wireless communication of the smart key system may be blocked by CXPI communication.

If an attempt is made to suppress emission of noise by performing control to reduce the slew rate of the bus signal mBUS and to make the bus signal mBUS rise and fall more gradually, then when the slave node 1504 transmits data, the fall of the bus signal sBUS input into the communication bus 1507 needs to be somewhat steeper for signal accuracy. On the other hand, if the fall of the bus signal sBUS is too steep, conduction noise is generated due to the change in the current flowing in the communication bus 1507. The conduction noise generated in the communication bus 1507 and the reason why the fall of the bus signal sBUS should not be made too gradual are now described with respect to FIG. 20, FIG. 21, FIG. 22, and FIG. 23.

FIG. 20 illustrates an example of a voltage signal on the communication bus 1507, and FIG. 21 illustrates an example of current flowing in the communication bus 1507. FIG. 22 schematically illustrates an example of current flow in the communication bus 1507.

When the bus signal sBUS from the slave node 1504 is not input to the communication bus 1507 and the bus signal mBUS from the master node 1501 is falling (interval Z₄ in FIG. 20 and FIG. 21), the current flows from the pull-up resistor side to the transistor Tr side in the CXPI transceiver 1503 as illustrated in (1) of FIG. 22, without flowing to the communication bus 1507.

As described with reference to FIG. 18, the slave node 1504 sets the voltage level of the bus signal sBUS on the communication bus 1507 to a low level. Therefore, upon inputting the transmission data signal TXD to the communication bus 1507 (interval Z₅ in FIG. 20 and FIG. 21), the current flows in the CXPI transceiver 1503 as indicated by (1) of FIG. 22 and also flows to the CXPI transceiver 1506 as indicated by (2). In other words, at this time, current flows in the communication bus 1507. When transitioning in this way from interval Z₄ to interval Z₅, conduction noise is generated due to the change in the current. The bus signal sBUS input to the communication bus 1507 at this time has a steeper inclination at the falling edge than the falling edge of the bus signal mBUS output from the master node 1501, as illustrated in FIG. 20. Therefore, a sudden change in current occurs.

Furthermore, when the bus signal mBUS output by the master node 1501 is high level and the voltage level of the bus signal sBUS output from the slave node 1504 is maintained at low level (interval Z₆ in FIG. 20 and FIG. 21), the current stops flowing to the transistor Tr side of the CXPI transceiver 1503, and as indicated by (2) in FIG. 22, all of the current flows from the pull-up resistor side of the CXPI transceiver 1503 to the CXPI transceiver 1506. Accordingly, the current flowing in the communication bus 1507 changes (increases) when transitioning from interval Z₅ to interval Z₆ as well, and conduction noise is therefore generated due to the change in the current.

FIG. 23 illustrates an example of the case when the inclination of the fall is set to be identical in the bus signal mBUS output by the master node 1501 and the bus signal sBUS output by the slave node 1504. When the inclination of the fall of the bus signal sBUS output from the slave node 1504 is gradual, then in the bus signal BUS, which is a combination of the bus signal mBUS from the master node 1501 and the bus signal sBUS from the slave node 1504 and which flows in the communication bus 1507, an interval Z₇ may occur, in which the signal level rises and falls in correspondence with the rise of the bus signal mBUS from the master node 1501 and the fall of the bus signal sBUS from the slave node 1504. If an interval Z₇ occurs in which the signal level rises and falls in this way, communication between the master node 1501 and the slave node 1504 becomes unstable. Therefore, in order to prevent such an interval Z₇ from occurring, the fall of the bus signal sBUS output from the slave node 1504 should have a certain degree of steepness.

On the other hand, upon making the fall of the bus signal sBUS output from the slave node 1504 steep, conduction noise occurs as described above, which may for example block wireless communication in a smart key system or the like.

An embodiment for reducing the effect of the aforementioned conduction noise is described below with reference to the drawings.

First, the principle in this embodiment behind reducing the effect of conduction noise is described with reference to FIG. 1. FIG. 1 illustrates the relationship between control by a slave node and current flowing in the communication bus. FIG. 1 illustrates a bus signal mBUS output by the master node 1501, a bus signal sBUS output by the slave node 1504, a bus signal BUS that is a combination of the bus signal mBUS and the bus signal sBUS, and the current I_(BUS) flowing in the communication bus 1507. In FIG. 1, time t₁ indicates the point in time at which the logical value of the bus signal sBUS from the slave node 1504 reaches 0 (slave fall end), and time t₂ indicates the point in time at which the bus signal mBUS from the master node 1501 starts to be displaced from the low level to the high level (clock rise start).

As described with reference to FIGS. 20 to 22, the current I_(BUS) flowing in the communication bus 1507 changes due to the operations when the slave node 1504 transmits data. In FIG. 1, section A indicates the change in the current I_(BUS) due to the transition from interval Z₄ to interval Z₅ in FIGS. 20 and 21, and section B indicates the change in the current I_(BUS) due to the transition from interval Z₅ to interval Z₆ in FIGS. 20 and 21.

When a time difference t_(diff) is a predetermined length, where t_(diff) is the difference between time t₂ and time t₁, then in a specific frequency band, a component of the current spectrum in section A and a component of the current spectrum in section B are canceled due to a phase relationship. In other words, in the components of the spectrum at each frequency band for section A and section B, the components of the frequency band for which the phase difference is π radians (or an odd multiple of π radians) cancel each other.

The relationship between the time difference t_(diff) and the frequency f_(notch) that is cancelled is now described in detail.

The phase difference Δϕ in the frequency components of section A and section B at a predetermined frequency f is represented by Equation (3) below. Δϕ=2π·t _(diff) ·f  (3)

In order for the components of section A and section B at frequency f_(notch) to be canceled, it suffices for the phase difference Δϕ to be an odd multiple of π radians. In other words, it suffices for Equation (4) to hold, where n is a natural number. 2π·t _(diff) ·f _(notch)=(2n−1)π  (4)

Solving Equation (4) for f_(notch) and t_(diff) yields Equation (5) and Equation (6) below. f _(notch)=(2n−1)/(2t _(diff))  (5) t _(diff)=(2n−1)/(2f _(notch))  (6)

Accordingly, by controlling the time difference t_(diff) to be the value calculated by substituting the frequency f_(notch) at which the spectrum components are cancelled into Equation (6) above, the effect of the harmonic at the frequency f_(notch) can be reduced.

FIG. 2 illustrates an example of the frequency spectrum of harmonic levels when executing control according to this embodiment. FIG. 2 illustrates the frequency spectrum of harmonic levels when the time difference t_(diff) is controlled to be the value calculated from Equation (6) with f_(notch)=134 kHz. As illustrated in FIG. 2, the harmonic level near f_(notch)=134 kHz indicated in the region 200 is reduced as compared to FIG. 19. As a result, the effect of conduction noise at the frequency band near f_(notch) can be reduced. In the example illustrated in FIG. 2, the case of f_(notch)=134 kHz has been described, but in other frequency bands as well, the harmonic level in the frequency band can be lowered by controlling the time difference t_(diff) to be the value calculated by Equation (6). As the difference in height (i.e. the fluctuation range of the current) between section A and section B is smaller, the effect of the reduction in the harmonic level increases.

FIG. 3 is a block diagram illustrating an example of a slave node transceiver for communication (CXPI transceiver 1506), according to this embodiment, which can reduce the above-described harmonic level. The CXPI transceiver 1506 includes an analog block 301 and a logic block 305.

The analog block 301 includes a driver 302, a receiver 303, and a clock rise start detector 304. The driver 302 inputs the transmission data signal TXD from the microcontroller 1505, acquired via the logic block 305, into the communication bus 1507. The receiver 303 acquires the bus signal mBUS input from the communication bus 1507 connected to the analog block 301 and transmits the bus signal mBUS to the logic block 305.

The clock rise start detector 304 is a circuit that detects the point in time at which the clock signal starts to be displaced from the low level to the high level, i.e. the time t₂. The clock rise start detector 304 is, for example, configured with a comparator. When the clock rise start detector 304 is configured with a comparator, for example the low level voltage V_(L) of the bus signal mBUS and the bus signal mBUS are input into the clock rise start detector 304. The clock rise start detector 304 compares the voltage V_(L) with the voltage of the bus signal mBUS that are input and outputs a signal representing the comparison result.

The logic block 305 includes a decoder 306, a clock rise start determiner 307, a transmission data signal delay adjuster 308, and an encoder 309. The decoder 306 transmits the result of decoding the signal acquired from the receiver 303 to the microcontroller 1505.

Based on the timing of the clock rise start acquired from the clock rise start detector 304, the clock rise start determiner 307 determines the time t₂ at which the bus signal mBUS starts to be displaced from the low level. Based on the time t₂ acquired from the clock rise start determiner 307 and on the target time difference t_(diff), the transmission data signal delay adjuster 308 determines the timing for inputting the transmission data signal TXD, i.e. the timing for lowering the bus signal sBUS from the slave node 1504.

The encoder 309 converts the data signal sTXD acquired from the microcontroller 1505 to a PWM signal and inputs the transmission data signal TXD to the driver 302. At this time, the encoder 309 inputs the transmission data signal TXD to the driver 302 at a predetermined timing based on the timing for inputting the transmission data signal TXD determined by the transmission data signal delay adjuster 308.

With reference to FIG. 4, the following describes control by the CXPI transceiver 1506 described with reference to FIG. 3. Like FIG. 1, FIG. 4 illustrates a bus signal mBUS output by the master node 1501, a bus signal sBUS output by the slave node 1504, a bus signal BUS that is a combination of the bus signal mBUS and the bus signal sBUS, and the current I_(BUS) flowing in the communication bus 1507. Here, an example of the case of the CXPI transceiver 1506 outputting the bus signal sBUS by transmitting the transmission data signal TXD at the n^(th) clock cycle is described.

First, with the clock rise start detector 304, the CXPI transceiver 1506 detects the time t_(2_n-1) of the clock rise start at the (n−1)^(th) cycle that is one cycle before the n^(th) cycle. With the clock rise start determiner 307, the CXPI transceiver 1506 also determines, based on the period T_(per) of the bus signal mBUS, the time t_(2_n)=t_(2_n-1) T_(per) of the n^(th) clock rise start from the detected time t_(2_n-1). Note that the CXPI transceiver 1506 need not detect the time t_(2_n-1) if the time t_(2_n) of the n^(th) clock rise start can be calculated. For example, the CXPI transceiver 1506 may calculate the time based on the time t_(2_n-m) of the (n−m)^(th) clock rise start (where n>m).

The CXPI transceiver 1506 subtracts the time difference tiff from the time with the transmission data signal delay adjuster 308, thereby calculating the time at which the logical value of the bus signal sBUS became 0, i.e. the time t_(1_n) of the slave fall end. The CXPI transceiver 1506 modulates the bus signal sBUS with logical value 0 to a PWM signal so that the time t_(1_n) becomes the slave fall end of the bus signal sBUS.

In this way, by the CXPI transceiver 1506 controlling the timing of control of the bus signal sBUS, the harmonic level at a predetermined frequency f_(notch) can be reduced.

Next, a modification to the CXPI transceiver 1506 of this embodiment is described. The modification described here is an example that can control the timing of the below-described slave fall end and the fall end (clock fall end) of the bus signal mBUS.

FIG. 5 illustrates the change in current of the communication bus when the slave fall end is sooner than the clock fall end. As illustrated in FIG. 5, when the time t₁ of the slave fall end of the bus signal sBUS is earlier than the time t₀ of the clock fall end of the bus signal mBUS, then from the time t₁ to the time t₀, all of the current flows from the pull-up resistor side of the master node 1501 to the slave node 1504 via the communication bus 1507. Therefore, a change in the current I_(BUS) of the communication bus 1507 occurs. Conduction noise is generated due to this change in current I_(BUS). The amount of change in the current I_(BUS) at this time is the total of the amount of change in section A and section B in FIG. 1. Therefore, the effect on conduction noise at this time increases more in comparison to section A and section B in FIG. 1. Accordingly, the time t₁ of the slave fall end should preferably be later than the time t₀ of clock fall end.

FIG. 6 is a block diagram illustrating an example of a transceiver for communication (CXPI transceiver 1506) according to a modification to this embodiment. The CXPI transceiver 1506 according to this modification includes an analog block 601 and a logic block 605.

The analog block 601 includes a driver 602, a first comparator 603, and a second comparator 604. The driver 602 inputs the transmission data signal TXD from the microcontroller 1505, acquired via the logic block 605, into the communication bus 1507.

The first comparator 603 and the second comparator 604 output a signal used in the logic block 605 to determine the time of the clock rise start and the clock fall end. The bus signal mBUS from the communication bus 1507 is input into the first comparator 603 and the second comparator 604. Furthermore, a first reference voltage V_(th1) is input into the first comparator 603, and a second reference voltage V_(th2) is input into the second comparator 604. The first reference voltage V_(th1) and the second reference voltage V_(th2) are each equal to or greater than the voltage V_(L) of the low level and equal to or less than the voltage V_(H) of the high level of the bus signal mBUS. It is assumed here that V_(th1)>V_(th2). The first comparator 603 and the second comparator 604 respectively compare the first reference voltage V_(th1) and the second reference voltage V_(th2) with the voltage of the bus signal mBUS and output a signal representing the comparison result (comparison signal).

The logic block 605 includes a clock rise start determiner 606, a clock fall end determiner 607, a transmission data signal delay adjuster 608, and an encoder 609.

The comparison signals from the first comparator 603 and the second comparator 604 are input into the clock rise start determiner 606 and the clock fall end determiner 607. Based on the acquired signal, the clock rise start determiner 606 determines the time t₂ at which the bus signal mBUS starts to be displaced from the low level. Based on the acquired signal, the clock fall end determiner 607 determines the time t₀ at which the bus signal mBUS reaches the low level. Details on the method by which the clock rise start determiner 606 and the clock fall end determiner 607 determine the time t₂ and the time t₀ are provided below.

Based on the time t₂ acquired from the clock rise start determiner 606, the time t₀ acquired from the clock fall end determiner 607, and the target time difference t_(diff), the transmission data signal delay adjuster 608 determines the timing for inputting the transmission data signal TXD. The transmission data signal delay adjuster 608 performs control so that the time t₁ of the slave fall end is earlier than the time t₂ of the clock rise start by the time difference t_(diff) that allows the desired harmonic level to be reduced. When the time t₁ is earlier than the time t₀ of the clock fall end, however, conduction noise is generated for the reason described with reference to FIG. 5. In order to avoid this conduction noise, the time t₁ of the slave fall end may be controlled to be at or later than the time t₀.

The encoder 609 converts the data signal sTXD acquired from the microcontroller 1505 to a PWM signal and inputs the transmission data signal TXD to the driver 602. The encoder 609 inputs the transmission data signal TXD acquired from the microcontroller 1505 to the driver 602 at a predetermined timing based on the timing for inputting the transmission data signal TXD determined by the transmission data signal delay adjuster 608.

Details on the method by which the clock rise start determiner 606 and the clock fall end determiner 607 determine the time t₂ of the clock rise start and the time t₀ of the clock fall end are now described with reference to FIG. 7. FIG. 7 illustrates the bus signal mBUS, a comparison signal Comp1 of the first comparator 603, and a comparison signal Comp2 of the second comparator 604.

From the comparison signal Comp1 of the first comparator 603 and the comparison signal Comp2 of the second comparator 604, the clock rise start determiner 606 determines a time t_(r1) at which the bus signal mBUS reached the voltage V_(th2) and a time t_(r2) at which the bus signal mBUS reached the voltage V_(th1) while transitioning from low level to high level. Based on the voltages V_(th2) and V_(th1) of the bus signal mBUS and the times t_(r1) and t_(r2), the clock rise start determiner 606 can calculate the rate of change of the bus signal mBUS. Specifically, the rate of change is calculated as (V_(th1)−V_(th2))/(t_(r2)−t_(r1)). Based on the calculated rate of change, the clock rise start determiner 606 calculates the time t₂ at which the voltage of the bus signal mBUS is the low level voltage V_(L). Specifically, the time t₂ is calculated by Equation (7) below, where V_(L)=0 and the time t_(r2) is the reference time. t ₂ =t _(r2)−(t _(r2) −t _(r1))·V _(th1)/(V _(th1) −V _(th2))  (7)

From the comparison signal Comp1 of the first comparator 603 and the comparison signal Comp2 of the second comparator 604, the clock fall end determiner 607 determines a time t_(f1) at which the bus signal mBUS reached the voltage V_(th1) and a time t_(f2) at which the bus signal mBUS reached the voltage V_(th2) while transitioning from high level to low level. Based on the voltages V_(th1) and V_(th2) of the bus signal mBUS and the times t_(f1) and t_(f2), the clock fall end determiner 607 can calculate the rate of change of the bus signal mBUS. Specifically, the rate of change is calculated as (V_(th2)−V_(th1))/(t_(f2)−t_(f1)). Based on the calculated rate of change, the clock fall end determiner 607 calculates the time t₀ at which the voltage of the bus signal mBUS is the low level voltage V_(L). Specifically, the time t₀ is calculated by Equation (8) below, where V_(L)=0 and the time t_(f1) is the reference time. t ₀=(t _(f2) −t _(f1))·V _(th1)/(V _(th1) −V _(th2))  (8)

The following describes control by the CXPI transceiver 1506 described with reference to FIG. 6. Here, an example of the case of the CXPI transceiver 1506 outputting the bus signal sBUS by transmitting the transmission data signal TXD at the n^(th) clock cycle is described.

First, the CXPI transceiver 1506 determines the time t_(2_n) of the n^(th) clock rise start with the clock rise start determiner 606. The method for determination of the clock rise start determiner 606 is similar to the method described in FIG. 4. Hence, details are omitted here. When determining the time t_(2_n), the clock rise start determiner 606 can determine the time of the clock rise start with the method described with reference to FIG. 7.

Next, with the clock fall end determiner 607, the CXPI transceiver 1506 determines the time t_(0_n) of the n^(th) clock fall end of the bus signal mBUS. Specifically, as illustrated in FIG. 8, the clock fall end determiner 607 detects the time t_(0_n-1) of the clock fall end of the bus signal mBUS at the (n−1)^(th) cycle that is one cycle before the n^(th) cycle. The clock fall end determiner 607 detects the time t_(0_n-1) with the method described with reference to FIG. 7. With the clock fall end determiner 607, the CXPI transceiver 1506 also determines, based on the period T_(per) of the bus signal mBUS, the time t_(0_n)=t_(0_n-1)+T_(per) of the n^(th) clock fall end of the bus signal mBUS from the detected time t_(0_n-1). Note that the CXPI transceiver 1506 need not detect the time t_(0_n-1) if the time t_(0_n) of the n^(th) clock fall end of the bus signal mBUS can be calculated. For example, the CXPI transceiver 1506 may calculate the time t_(0_n) based on the time t_(0_n-m) of the (n−m)^(th) clock fall end of the bus signal mBUS (where n>m).

The CXPI transceiver 1506 also determines the time of the delay of the transmission data signal TXD with the transmission data signal delay adjuster 608. Details on the method by which the transmission data signal delay adjuster 608 determines the delay time are provided with reference to FIG. 9 and FIG. 10.

FIG. 9 and FIG. 10 illustrate an example of a method by which the transmission data signal delay adjuster in FIG. 6 determines the delay time. FIG. 9 and FIG. 10 illustrate the bus signal mBUS, the transmission data signal TXD (not controlled) when not controlling the timing of output, and the transmission data signal TXD when controlling the timing of output. Here, the time t_(f1) at which the voltage becomes V_(th1) when the bus signal mBUS falls is described as being a reference time.

In FIGS. 9 and 10, D_(int) is a delay value within the circuit and includes a comparator delay, an internal circuit delay, a bus output delay, and the like. Furthermore, t_(d1y) is the delay time.

When the time difference t_(diff) is equal to or less than the time between the time t₂ and the time t₀, i.e. when t_(diff)≤t₂−t₀, the transmission data signal delay adjuster 608 determines t_(d1y) by Equation (9) below. t _(d1y)=(t ₂ −t _(diff))−D _(int)  (9) FIG. 9 illustrates an example of a state in which Equation (9) holds.

When the time difference t_(diff) is longer than the time between the time t₂ and the time t₀, i.e. when t_(diff)>t₂−t₀, the transmission data signal delay adjuster 608 determines t_(d1y) to be a value satisfying Equation (10) below, where t_(min)=t₀−D_(int). t _(d1y) >t _(min)  (10)

In this way, when t_(diff)>t₂−t₀, by setting t_(d1y) to be a value larger than t_(min), generation of the conduction noise described with reference to FIG. 5 can be avoided.

With the encoder 609, the CXPI transceiver 1506 controls the transmission data signal TXD based on the calculated delay time t_(d1y). FIG. 11 and FIG. 12 illustrate the transmission data signal TXD controlled by the encoder 609 in FIG. 6, and the bus signal BUS yielded by combining the bus signal mBUS and the bus signal sBUS. FIG. 11 illustrates the results of control when t_(diff)≤t₂−t₀, and FIG. 12 illustrates the results of control when t_(diff)>t₂−t₀.

At the delay time corresponding to t_(d1y), the encoder 609 converts the transmission data signal TXD with logical value 0 to a PWM signal and outputs the result. At this time, with respect to the fall of the transmission data signal TXD, the encoder 609 performs control for a time delay corresponding to t_(d1y). On the other hand, with respect to the time at which the transmission data signal TXD starts to rise (slave rise start), the encoder 609 performs control so that the length of time from the time t₀ is a constant length of time. Assuming that the fall of the bus signal mBUS is constant, the encoder 609 controls the transmission data signal to rise after a constant length of time from the time t₀. In this way, the CXPI transceiver 1506 can reduce the harmonic level at a desired frequency band while maintaining the duty cycle of the bus signal BUS.

If the time t₁ of the slave fall end is later than the time t₂ at which the clock signal starts to be displaced from the low level to the high level, then the current flowing in the communication bus 1507 suddenly changes as illustrated in FIG. 13, generating conduction noise. Accordingly, the time t₁ should preferably be earlier than the time t₂. According to the above-described embodiment and modification, the time t₁ is controlled to be earlier than the time t₂.

Although embodiments of this disclosure have been described based on examples and on the accompanying drawings, it is to be noted that various changes and modifications will be apparent to those skilled in the art based on this disclosure. Therefore, such changes and modifications are to be understood as included within the scope of this disclosure. For example, the functions and the like included in the structural components may be reordered in any logically coherent way. Furthermore, structural components and the like may be combined into one or divided.

For example, in the above-described embodiment and modification, the encoder may generate a PWM signal, and a timing adjustment circuit provided separately in the CXPI transceiver 1506 may perform control to delay the falling edge of the control signal (slave fall end). In the above-described embodiment and modification, the function of the timing adjustment circuit has been described as being included in the encoder.

The above-described clock rise start determiner 307, transmission data signal delay adjuster 308, clock rise start determiner 606, clock fall end determiner 607, and transmission data signal delay adjuster 608, for example, may be configured as a logic circuit or the like in which a plurality of logic cells are combined. Specific examples include one or more of each of the following: an Application Specific Integrated Circuit (ASIC), Digital Signal Processor (DSP), Digital Signal Processing Device (DSPD), Programmable Logical Device (PLD), Field Programmable Array (FPGA), System-on-Chip (SoC), processor, controller, microcontroller, and microprocessor, or a combination thereof.

Various embodiments described herein may include various operations. These operations may be performed and/or controlled by hardware components, digital hardware and/or firmware, and/or combinations thereof. As used herein, the term “coupled to” may mean coupled directly or indirectly through one or more intervening components. Any of the signals described herein may be time multiplexed with other signals and provided over one or more common buses. Additionally, the interconnection between circuit components or blocks may be shown as buses or as single signal lines. Each of the buses may alternatively be one or more single signal lines and each of the single signal lines may alternatively be buses.

Certain embodiments may be implemented as a firmware or software product that may include instructions stored on a non-transitory computer-readable medium, e.g., such as volatile memory and/or non-volatile memory. These instructions may be used to program one or more devices that include one or more general-purpose or special-purpose processors (e.g., such as CPUs, ASICs, DSPs, DSPDs, PLDs, FPGAs, SoCs, etc.) or equivalents thereof (e.g., such as processing cores, processing engines, microcontrollers, and the like), so that when executed by the processor(s) or the equivalents thereof, the instructions cause the device(s) to perform the operations described herein. A non-transitory computer-readable storage medium may include, but is not limited to, electromagnetic storage medium (e.g., floppy disks, hard disks, and the like), optical storage medium (e.g., CD-ROM), magneto-optical storage medium, read-only memory (ROM), random-access memory (RAM), erasable programmable memory (e.g., EPROM and EEPROM), flash memory, or another now-known or later-developed non-transitory type of medium that is suitable for storing information. A computer-readable medium may also include one or more mechanisms for storing or transmitting information in a form (e.g., software, processing application, etc.) that is readable by a machine (e.g., such as a device or a computer).

In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense. 

What is claimed is:
 1. A communication system comprising: a clock extension peripheral interface (CXPI) communication bus; a master node coupled to the CXPI communication bus and configured to transmit a reference clock signal thereon; and a plurality of slave nodes coupled to the CXPI communication bus and configured to receive the reference clock signal, wherein each slave node of the plurality of slave nodes comprises: a timing circuit configured to determine a first time based on a detected rise of the reference clock signal from low level to high level; a delay adjuster circuit configured to determine a second time based on the first time and a predetermined time difference value; and an encoder circuit configured to extend the low level of the reference clock signal by changing a data signal to be output to the CXPI communication bus from the high level to the low level.
 2. The communication system of claim 1, wherein the delay adjuster circuit is configured to compute the predetermined time difference value based on a frequency at which a harmonic level is reduced and on a natural number.
 3. The communication system of claim 1, wherein the timing circuit comprises: a clock-rise detector circuit configured to detect a rising edge of the reference clock signal from the low level; and a clock-fall detector circuit configured to detect a falling edge of the reference clock signal from the high level.
 4. The communication system of claim 1, wherein the delay adjuster circuit is configured to determine the second time to be after a detected fall of the reference clock signal from the high level.
 5. The communication system of claim 1, wherein the delay adjuster circuit is configured to determine the second time to be earlier than the detected rise of the reference clock from the low level.
 6. The communication system of claim 1, wherein the reference clock signal is generated based on an internal clock signal of the master node.
 7. The communication system of claim 1, wherein the reference clock signal is used by each of the plurality of slave nodes to transmit and receive data on the CXPI communication bus.
 8. The communication system of claim 1, wherein the master node controls, through the reference clock signal, an operational timing of each slave node of the plurality of slave nodes.
 9. The communication system of claim 1, wherein the communication system is disposed in a vehicle.
 10. The communication system of claim 9, wherein the communication system further includes a smart key system.
 11. The communication system of claim 9, wherein the plurality of slave nodes are configured to control electronically-controllable devices of the vehicle.
 12. The communication system of claim 11, wherein the electronically-controllable devices of the vehicle include one or more of an air conditioner, a door mirror, a power window, and a window wiper.
 13. The communication system of claim 1, wherein the master node includes a microcontroller and a CXPI transceiver.
 14. The communication system of claim 13, wherein the microcontroller includes a Universal Asynchronous Receiver Transmitter (UART) interface to transmit and receive signals to and from the CXPI transceiver.
 15. The communication system of claim 13, wherein the master node is configured to transmit data on the CXPI communication bus based on the reference clock signal and on a data signal that is output from the microcontroller to the CXPI transceiver.
 16. The communication system of claim 13, wherein the CXPI transceiver includes a clock generation circuit that comprises: a pull-up resistor coupled between a power line and an output terminal of the CXPI transceiver, wherein the pull-up resistor is configured to generate the high level of the reference clock signal; and a transistor coupled between the output terminal of the CXPI transceiver and a ground line, wherein the transistor is controlled by a data signal to generate the low level of the reference clock signal, and wherein the data signal is output from the microcontroller to the CXPI transceiver.
 17. The communication system of claim 16 wherein, when output to the CXPI communication bus, the reference clock signal exhibits a logical value of 1 when the data signal is at the high level and a logical value of 0 when the data signal is the low level.
 18. The communication system of claim 1, wherein said each slave node of the plurality of slave nodes includes a respective microcontroller and a respective CXPI transceiver.
 19. The communication system of claim 18, wherein the respective microcontroller includes a Universal Asynchronous Receiver Transmitter (UART) interface to transmit and receive signals to and from the respective CXPI transceiver, within said each slave node.
 20. The communication system of claim 18, wherein the respective CXPI transceiver includes the timing circuit, the delay adjuster circuit and the encoder circuit, within said each slave node. 